/**
 * Software License, Version 1.0
 * 
 * Copyright 2003 The Trustees of Indiana University.  All rights reserved.
 * 
 *
 *Redistribution and use in source and binary forms, with or without 
 *modification, are permitted provided that the following conditions are met:
 *
 *1) All redistributions of source code must retain the above copyright notice,
 * the list of authors in the original source code, this list of conditions and
 * the disclaimer listed in this license;
 *2) All redistributions in binary form must reproduce the above copyright 
 * notice, this list of conditions and the disclaimer listed in this license in
 * the documentation and/or other materials provided with the distribution;
 *3) Any documentation included with all redistributions must include the 
 * following acknowledgement:
 *
 *"This product includes software developed by the Community Grids Lab. For 
 * further information contact the Community Grids Lab at 
 * http://communitygrids.iu.edu/."
 *
 * Alternatively, this acknowledgement may appear in the software itself, and 
 * wherever such third-party acknowledgments normally appear.
 * 
 *4) The name Indiana University or Community Grids Lab or NaradaBrokering, 
 * shall not be used to endorse or promote products derived from this software 
 * without prior written permission from Indiana University.  For written 
 * permission, please contact the Advanced Research and Technology Institute 
 * ("ARTI") at 351 West 10th Street, Indianapolis, Indiana 46202.
 *5) Products derived from this software may not be called NaradaBrokering, 
 * nor may Indiana University or Community Grids Lab or NaradaBrokering appear
 * in their name, without prior written permission of ARTI.
 * 
 *
 * Indiana University provides no reassurances that the source code provided 
 * does not infringe the patent or any other intellectual property rights of 
 * any other entity.  Indiana University disclaims any liability to any 
 * recipient for claims brought by any other entity based on infringement of 
 * intellectual property rights or otherwise.  
 *
 *LICENSEE UNDERSTANDS THAT SOFTWARE IS PROVIDED "AS IS" FOR WHICH NO 
 *WARRANTIES AS TO CAPABILITIES OR ACCURACY ARE MADE. INDIANA UNIVERSITY GIVES
 *NO WARRANTIES AND MAKES NO REPRESENTATION THAT SOFTWARE IS FREE OF 
 *INFRINGEMENT OF THIRD PARTY PATENT, COPYRIGHT, OR OTHER PROPRIETARY RIGHTS. 
 *INDIANA UNIVERSITY MAKES NO WARRANTIES THAT SOFTWARE IS FREE FROM "BUGS", 
 *"VIRUSES", "TROJAN HORSES", "TRAP DOORS", "WORMS", OR OTHER HARMFUL CODE.  
 *LICENSEE ASSUMES THE ENTIRE RISK AS TO THE PERFORMANCE OF SOFTWARE AND/OR 
 *ASSOCIATED MATERIALS, AND TO THE PERFORMANCE AND VALIDITY OF INFORMATION 
 *GENERATED USING SOFTWARE.
 */

package cgl.narada.util;

import java.util.Hashtable;
import java.util.Vector;

/**
 * A Hashqueue is a FIFO queue based on Hashtable. We can limit the size of queue hence its a queue,
 * Entities in the queue can be accessed by using a key hence entries can be accessed using a
 * hashtable interface. If the size of the queue is greater than the specified value 'N', future
 * additions would cause removal of items which came in first (FIFO). <br>
 * Created on Mar 31, 2005
 * 
 * @author Harshawardhan Gadgil (hgadgil@grids.ucs.indiana.edu)
 */

public class HashQueue {

    Hashtable itemTable;

    Vector keyTable;

    private int MAX_SIZE;

    public HashQueue(int _size) {
        MAX_SIZE = _size;
        keyTable = new Vector();
        itemTable = new Hashtable();
    }

    public synchronized void put(Object key, Object object) {

        // = comparison is OK since all entries must be added thru here only.
        if (keyTable.size() == MAX_SIZE) {
            Object o = keyTable.remove(0);
            itemTable.remove(o);
        }

        itemTable.put(key, object);
        keyTable.add(key);
    }

    public void clear() {
        keyTable.clear();
        itemTable.clear();
    }
    
    public synchronized Object get(Object key) {
        return itemTable.get(key);
    }

    public synchronized Object remove(Object key) {
        if (keyTable.contains(key)) {
            keyTable.remove(key);
            return itemTable.remove(key);
        }
        return null;
    }

    public boolean containsKey(Object key) {
        return itemTable.containsKey(key);
    }
}